The field of the invention is photography combined with the compound lens system of a microscope and the invention is particularly concerned with a microscope attachment camera with exposure metering for the photographic recording of an object or detail of same.
The state of the art of microscope attachment cameras may be ascertained by reference to U.S. Pat. No. 4,118,719 of the present inventors. U.S. Pat. No. 4,118,719 is incorporated herein because the present invention is an improvement thereover and like components are designated with the same reference numerals.
U.S. Pat. No. 4,118,719 discloses an attachment camera for microscopes having an observation beam with a system for measuring the brightness of an object detail and with markings for sighting at least the detail metering field and the image field of the camera in the observation beam. Markings for the metering field and for the image field are mounted on two separate plates. The metering field marking plate is defined by a metering field stop, and the two markings, which differ in shape and size, are reflected simultaneously be means of a photographic ocular located in the picture-taking beam and by optical components arranged ahead or behind the photographic ocular and comprising partly or wholly specular surfaces.
When a photographic ocular is changed, there is also a change of the marked field on the reticle (image field marking plate) on account of the change in magnification. When a photographic ocular is selectively used having a different magnification, the reticle which defines the image field therefore also requires corresponding markings for the different magnification stage. When a zoom photographic ocular is used, the conventional calibration of image formats on reticles cannot be implemented in a technically meaningful way since a large number of markings is required which could be used in the particular case applied only with very great difficulty. Furthermore, all intermediate positions are then merely estimated.
Besides the solution of the problem disclosed and defined in U.S. Pat. No. 4,118,719, apparatus is already known which in addition to viewing through the microscope tube proper also provides a separate adjusting telescope. While in this prior art device multiple markings on the reticle are avoided, on the other hand, a basic drawback is also thereby introduced: the operation of such attachment cameras is hampered by the fact that the observer must constantly look through the microscope tube proper and then through the separate adjusting telescope (camera viewing) and vice versa. The two tube microscope is disclosed in U.S. Pat. No. 3,987,463 and U.S. Pat. No. 4,006,487.
Lastly, photographic microscopes are known in which the picture taking field is superposed as a luminous frame on the microscope image. In this case, there is no change in the photographic oculars. Instead, optical systems are mounted between the objective and the microscope tube which change the magnification either stepwise or continuously. The drawback of these systems is that when a picture is taken of a rather small image detail, the overall magnification is increased and hence, the visible object field is reduced. An example of such a system is disclosed in U.S. Pat. No. 4,057,318.
Furthermore, all prior art apparatus suffer from the drawback that the object must be rotated, for instance by means of a turntable, in order to align the object structures with the boundary of the image field markings.